1. Field of the Invention
The present invention relates to an imaging apparatus that records moving images, and to a reproducing apparatus that reproduces the moving images, such as a video camera or a digital camera.
2. Description of the Related Art
In recent years, a recording and reproducing apparatus capable of recording/reproducing high-quality video signals such as high definition (HD) video signals or HD signals, and a video display apparatus capable of displaying such signals as images have been widely spread. Background techniques of an image processing system used in these apparatuses include techniques of miniaturizing the size of an image sensor, increasing the number of pixels, increasing the speed of transfer processing, and improving the efficiency of coding such as the H.264 standard. In addition, various types of video display apparatuses have been made available, such as those of a liquid crystal type, a plasma type, and an electro-luminous (EL) type. Further, video display apparatuses having a further decreased thickness, a higher definition, and/or a larger screen are being developed. Mobile-type video display apparatuses are also being developed.
Since display apparatuses of such various types have been become available, users' viewing styles have changed significantly. Users handle images in various manners depending on the purpose, for example, some users prefer high-quality images while others wish to exchange short movies with ease.
Techniques for storing large amounts of video data play an important role in addressing the needs of users. Particularly, remarkable progress has been made in the increase of the capacity of hard disks and in the decrease of costs thereof, followed by semiconductor memories. Additionally, large-capacity removable media or servers on the order of terabytes have been made available at low cost.
Under the background described above, while the frame rate of the national television system committee (NTSC) is 29.97 frames/second in the field of imaging techniques, higher frame rates such as 120 frames/second and 240 frames/second are proposed. Further, techniques for multi-screen reproduction and reproduction with multi-audio channels are also being developed. Based on these techniques, more realistic and dynamic images can be displayed.
While video signals are conventionally recorded at a fixed frame rate, some techniques are proposed for appropriately changing the frame rate, efficiently suppressing the total amount of recording data, and recording high-quality videos when necessary.
Japanese Patent Application Laid-Open No. 2003-274360 (U.S. Pat. No. 7,456,875) discusses a technique for controlling the frame rate of captured video signals without requiring a photographer's control. More specifically, based on this technique, when an image is captured, a surrounding audio volume level is monitored, and if it is detected that the monitored volume level exceeds a predetermined level, the frame rate is increased, so that important scenes are recorded with high quality. Further, based on this technique, when the available memory capacity of a recording medium reaches less than or equal to a predetermined level, the frame rate is decreased to suppress consumption of the recording medium. In addition, when the available power of a battery reaches less than or equal to a predetermined level, the frame rate is decreased to suppress consumption of the battery.
Japanese Patent Application Laid-Open No. 2007-134991 (USPA 2007/0104462) discusses a technique in which motion of a captured image is detected. Based on this technique, when the detected motion is more than or equal to a threshold, the captured image is recorded at a high frame rate, and when the detected motion is less than the threshold, the captured image is recorded at a low frame rate.
However, based on the above techniques discussed in Japanese Patent Application Laid-Open No. 2003-274360 (U.S. Pat. No. 7,456,875) and Japanese Patent Application Laid-Open No. 2007-134991 (USPA 2007/0104462), change of the frame rate does not reflect photographer's intention. Namely, based on the technique discussed in Japanese Patent Application Laid-Open No. 2003-274360 (U.S. Pat. No. 7,456,875), the frame rate is changed depending on conditions surrounding an imaging apparatus, such as the surrounding audio volume level or the available power of a recording medium or a battery. Thus, the imaging condition is changed without photographer's intention.
In addition, the technique discussed in Japanese Patent Application Laid-Open No. 2007-134991 (USDA 2007/0104462) uses motion information acquired from an image signal as an index. For example, when the ratio of monotonous scenes including the sky or night scenes is increased, it is determined that the amount of motion is less, and as a result, the image is recorded at a low frame rate. On the other hand, in a wide image whose focal length is short, the motion amount tends to be detected as being large because of camera shake, and consequently, the image is recorded at a high frame rate. In either case, the frame rate is determined irrespective of photographer's intention.
Normally, TV receivers or video monitors support only a fixed frame rate. Thus, when a video signal is input and the frame rate thereof is changed in the middle of processing, even if the change of the frame rate can be followed, the video may be displayed at an unnatural rendering speed misaligned with the actual time. For example, if a monitor receives an input video signal and displays the signal at a certain rate images captured at a frame rate higher than the standard frame rate are rendered in slow motion, and images captured at a lower frame rate are rendered at high speed.
Since compatibility between these viewing and reproduction environments is not taken into consideration, use of the technique of variable frame rate recording is limited.